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An integrated circuit that contains the entire central processing unit of a computer on a single chip.

The first microprocessors emerged in the early 1970s by Intel.

At the heart of all personal computers and most workstations sits a microprocessor.

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Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection system for automobiles.

Figure: Intel 4004, the first general-purpose, commercial microprocessor.

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TOPICS WE ARE GOING TO TOPICS WE ARE GOING TO COVER COVER

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The 6800 is an 8-bit microprocessor produced by Motorola and released shortly after the Intel 8080 in late 1974.

It had 78 instructions.

This microprocessor also had a couple of extra instructions added to it’s instruction sets.

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It may have been the first microprocessor with an index register.

It was usually packaged in a 40 pin DIP (dual-inline package).

Fig: Motorola 6800 microprocessor

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It's not clear if there was a chief architect, but the two main designers were Chuck Peddle and Charles Melear.

Charles Melear continued working at Motorola on the 6800 family and the 683xx family including the 68332.

Bill Mensch designed the MC6820 PIA (Peripheral Interface Adapter).

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microprocessor year

MOTOROLA 6800 1974

MOTOROLA 68000 1979

MOTOROLA 68020 1984

MOTOROLA 68030 1987

MOTOROLA 68040 1991

MOTOROLA 68020 1993

MOTOROLA POWER PC 603

1994

MOTOROLA POWER PC 604

1994

MOTOROLA POWER PC 620

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Introduced in 1975.

strictly an 8-bit processor capable of addressing 64 kilobytes of memory.

Main difference with Intel is to minimize the usage of registers in favor of general purpose RAM.

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The 6802 incorporated 128 bytes of RAM on the CPU itself.

The 6803/6808 ran faster (3.58 MHz), incorporated 128 bytes of RAM, and included both a URAT (universal asynchronous receiver or transmitter) for serial communications, and a counter/timer.

The last variation of the 8-bit Motorola family was the 6809. 11

By 1978, the age of the 16-bit CPU had begun.

In 1978 Motorola introduced its first 16-bit CPU: the 68000.

Unlike Intel’s 8086/8088, which could address only one megabyte of physical RAM, the 68000 had 24 address lines that could access 16 megabytes of RAM directly.12

The 68000 ran faster than mainstream Intel processors of that day: 16MHz.

Motorola abandoned the idea of RAM-based registers and incorporated 16 general-purpose registers in the 68000.

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Motorola entered the 32-bit CPU arena with the 68020.

The 68020 has 16 general-purpose registers, and can address four gigabytes of RAM directly.

It had an internal 256-byte instruction cache .

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The 68030 is Motorola’s second generation 32-bit CPU. It is available in faster speeds, and with one 256-byte cache each for data and instruction.

The 68040 is the third generation. It increases the data and instruction caches to 4 kilobyte each, includes an on-board math co-processor and memory management unit. 15

The latest members of the 680x0 family is the 68060.

68060 is a superscalar design that has multiple instruction pipelines and on board memory and power management.

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The PowerPC is the first implementation of reduced instruction act computing (RISC) for personal computers.

The MPC601, or PowerPC, is a 640bit superscalar CPU that can effectively execute up to three instructions per clock cycle.

It has a 32-bit address bus, 32 kilobytes of cache memory and an internal math co-processor.

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A 16-bit address bus provides the MC6800 with access to 65k bytes of memory.

Three-state operation of the data and address line is permitted.

The MPU (Memory protection unit) will respond to a set of 72 variable-length instructions.

MC6800 has seven address modes.18

Timing of the MPU is accomplished with a two-phase clock at rates of up to 1.0 MHz

It has four chip select inputs. The MC6800L, single-chip digital

modem, provides modulation, demodulation, and supervisory control functions, necessary to implement a serial data communications link.

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Three kinds of memory: Program memory Data memory Stack memory

Program, data and stack memories occupy the same memory space. The total addressable memory size is 64 KB.

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Reserved memory locations: FFF8h - FFF9h FFFAh – FFFBh FFFCh – FFFDh FFFEh - FFFFh

Some memory addresses are reserved for memory mapped I/O as the processor doesn't have hardware I/O capability.

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The MC6800 contains six program-available

registers . The 2-byte registers are: Program counter. Stack pointer. Index register.The single-byte registers are: Accumulators. Condition code register.

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Figure: Block diagram of MC6800 microprocessor.

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The MC6800 microprocessor has 40 Pins . According similarities all these pins are divided into five groups: Address/data bus. Start signal. Bus control signals. Interrupt signals. Direct Memory Access(DMA) signal.

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Figure : Pins ASSIGNMENT of MC6800 Microprocessor

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MC6800 Clocks: The MC6800 has four pins committed to

developing the clock signals needed for internal and system operation.

They are: 1.The oscillator pins EXTAL and XTAL2.The standard M6800 enable (E) clock3.Quadrature (Q) clock.

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SIGNAL DESCRIPTIONSIGNAL DESCRIPTION

Processor State Indicators :Two output lines to indicate the present

processor state. Bus available (BA) . Bus status (BS) .

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Address Bus (A0-A15): This is 16-bit,unidirectional. Three-state bus, to provide address

information to the address bus.

Data Bus (D0-D7): This is 8-bit, bidirectional. This three-state bus is the general purpose

data path.

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Read/Write (R/W): This output indicates the direction of data

transfer on the data bus.

Interrupts: Three separate interrupt input pins: Non- maskable interrupt (NMI) Fast interrupt request (FIRQ) Interrupt request (IRQ)

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Direct Memory Access/Bus Request: This input is used to suspend program

execution. This also makes the buses available for

another use such as a direct memory access or a dynamic memory refresh.

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The MC6800 has a set of 72 different executable

source instructions. They include: Data moving instructions. Arithmetic – add, subtract, negate,

increment, decrement and compare. Logic – AND, OR, exclusive OR,

complement, shift/rotate. Control transfer – conditional and

unconditional. Other – clear/set condition flags, bit test,

stack operations, software interrupt, etc. 31

The addressing modes available on the MC6809 and MC6809E are:

Inherent, Immediate Extended Direct Indexed Branch Relative.

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Figure: Programming model of MC6800.

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Only one pointer register.

Stack instructions use post-decrement on push and pre-increment on pop instead of the more natural post-increment on pop and pre-decrement on push.

index register can not be directly pushed or popped from the stack.

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The accumulators and index registers occupy different spaces and thus there are no instructions to transfer or operate between the two.

The CPX (compare X) instruction does not affect the Carry flag.

The DAA (decimal adjust) instruction only worked after addition, and not subtraction. 35

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